Data collected
from the National Highway Traffic Safety Administration survey in 2010.

Cutting calories with diet drinks may not be a good idea anymore — at least not at the bar.

According to a new study published Tuesday in the journal Alcoholism: Clinical and Experimental Research, mixing alcohol with a diet or sugar-free soft drink could result in a higher breath alcohol concentration compared with mixing alcohol with a regular sugared drink.

Cecile Marczinski, an assistant professor of psychology at Northern Kentucky University, was one of the lead researchers of the study. She specializes with energy drinks and their effects on the body when mixed with alcohol. Marczinski and her research team initiated the study when they noticed a higher level of breath alcohol content, or BrAC, in people – particularly women -- who had consumed diet drinks at a bar.

During the study, subjects were given one of three doses: vodka and diet soda, vodka and regular soda, and a placebo beverage that was made to smell like vodka. By using breath tests, which measure the alcohol exhaled from the lungs, Marczinski found that subjects who drank with a diet mixer had a BrAC that was 18 percent higher than those who consumed the same amount of alcohol with a sugar-sweetened drink. The cause starts with the digestive track and is the same reason health experts recommend eating a full meal before drinking alcohol.

“The stomach treated the sugary drink as food so it keeps it in the stomach longer to allow time for digestion,” she said. “Diet drinks contain no sugar, so it goes through the digestive track immediately, and the alcohol is then absorbed by the liver.”

Even though the study was small — eight males and eight females — the results reflected similar studies performed during field research. For the past decade, Dennis Thombs, a professor and chair of the department of behavioral and community health at University of North Texas Health Science Center, has been assessing and systematically sampling bar patrons on their way home.

“We found the same result,” Thombs said. “Those who drank diet drinks were more intoxicated than those who had consumed drinks with sugar-based soda.”

Thombs’ study also found a significant difference between the intoxication level of young men and women. He said this might be because women tend to be more weight conscious than men, and therefore women were more likely to specify that they wanted a diet soda.

“Women are probably wanting to consume healthier drinks that have less calories,” he said. “But they may not be aware that they’re getting more intoxicated than they intended to.”

Both Thombs and Marczinski agreed that the most frightening result of the study was that subjects were unaware of the difference in intoxication levels. Those who mixed diet drinks with alcohol had BrAC levels of .09, which is above the legal driving limit of .08, whereas those who mixed sugared sodas with alcohol averaged about .07.

“Both groups felt the same and both groups were willing to drive,” Marczinski said. “Choices to drink and drive often depend on how people feel rather than some objective measurement of impairment.”

Subjects were then asked to perform computer tests, which simulated situations that they might face behind the wheel while their reaction times and errors were measured. Those who drank with a diet mixer were more impaired and slower to react.

According to data from the National Highway Traffic Safety Administration, there were 927 reported deaths in Illinois due to traffic accidents in 2010. Approximately 32 percent — 292 deaths— was related to drunken driving. This number didn’t improve in 2011 with 926 total deaths with 278 related to drunken driving.

“Alcohol impairs judgment,” Marczinski said. “It’s not surprising that people are bad at judging how drunk they actually are when they’re drunk.”

Marczinski said she will likely follow up with more research in this area to examine different dose levels of alcohol. She said she would also like to focus on the different types of drinks to replicate in the lab what people are doing in real life, specifically if there are certain drink combos that are more problematic than others.

Thombs said he would continue his research as well because the results are not conclusive yet. There are only a few studies that have closely examined the link between someone’s level of intoxication and the type of mixer they use.

“For those of us who are interested in increasing the safety of the bar atmosphere, we need to take a closer look at alcohol mixers,” Thombs said. “Not just soda and diet soda but energy drinks as well.”